1. Technical Field
The present invention relates generally to a motorised handpiece for driving a tool which can be coupled to the handpiece. More particularly, the present invention relates to a motorised handpiece which can be used as a treatment handpiece used by dentists or an operating handpiece used by dental technicians.
2. Background Information
A motorised handpiece for operating a tool which can be coupled to the motorised handpiece, with a motor, with a clamping mechanism for clamping a tool in a force-locking manner, with a shaft arrangement for transmitting a rotary movement of the motor via the clamping mechanism to the clamped tool is known, for example, from DE-A1-44 06 855 and is illustrated in FIG. 5a.
The motorised handpiece 101 illustrated in FIG. 5a essentially comprises two handpiece parts 112, 113, a motor, in the illustrated example a collector-free d.c. motor, being arranged in the handpiece part 112, and a rapid clamping system for a dental tool, for example, being arranged in the other handpiece part 113. The collector-free d.c. motor comprises a short-circuit ring 102, a stator winding 103 and a rotor magnet 104. Current is supplied to the motor via a supply line 118. Furthermore, the rotor magnet 104 is fitted to a first shaft 109, the shaft 109 being rotatably mounted in the handpiece part 112 with the aid of two ball bearings 114, 115. The shaft 109 is thus set in rotation together with the rotor magnet 104 when the motor is actuated.
The rapid clamping system of the second handpiece part 113 essentially comprises a sleeve-shaped, slotted clamping jaw 105, which is arranged coaxially in the said handpiece part and is coupled to or forms part of a further drive shaft 110. At its outer end, the clamping jaw has a conical external shape, which matches a correspondingly shaped conical internal shape of a bearing sleeve 106, in which the clamping jaw 105 is arranged. The clamping jaw 105 is connected or coupled via an actuating mechanism (not shown) to the housing of the second handpiece part 113. The two handpiece parts 112 and 113 can be coupled to one another, more particularly screwed. The two handpiece parts 112 and 113 can be preferably screwed together in the form of a bayonet lock. The above-mentioned actuating mechanism can comprise a starting rod, for example, which upon rotation of the housing of the handpiece part 113 relative to the housing of the handpiece part 112 in a given direction produces an axial displacement of the clamping jaw 105 to the right, the latter being compressed with the increasing longitudinal displacement of the clamping jaw 105 as a result of the matching external and internal shapes of the clamping jaw 105 and the bearing sleeve 106, so that a tool 108, which is located in the clamping jaw 105 and of which only the tool shaft is indicated in FIG. 5a, is clamped in a force-locking manner in the clamping jaw 105. In this respect, the longitudinal displacement of the clamping jaw 105 to the right is effected against a spring force of a spring 107 schematically illustrated in FIG. 5a, which can be a cup or helical spring, for example. A rotation of the handpiece part 113 relative to the handpiece part 112 in the opposite direction accordingly results in a longitudinal displacement of the clamping jaw 105 to the left, which is supported by the spring force of the spring 107. This clamping mechanism is generally referred to as a control grip rapid clamping mechanism. For further details of the clamping mechanism, reference is made to DE-A1-44 06 855.
Of course, the control grip rapid clamping mechanism explained above can also be constructed in such a manner that, instead of the bearing sleeve 106, the clamping jaw 105 is non-displaceably arranged, whilst in contrast to FIG. 5a the bearing sleeve 106 is displaced in the longitudinal direction in synchronism with the rotation of the handpiece part 113 relative to the handpiece part 112.
It can be seen from FIG. 5a that the two handpiece parts 112 and 113 each comprises separate drive shafts 109, 110, which on the one hand are rotatably mounted with the aid of two ball bearings 114, 115 and 116, 117 respectively and on the other hand are coupled to one another via a mechanical driver system 111.
However, in the motorised handpiece shown in FIG. 5a there is a markedly increased production of noise in particular at high rotational speeds on account of unavoidable alignment errors resulting from the mechanical coupling of the two drive shafts 109, 110. Furthermore, a total of four ball bearings 114-117 is required for this motorised handpiece, which limit the rotational speed, in particular in cases where collector-free d.c. motors without additional cooling fans are used. However, it is desirable to dispense with additional cooling fans on account of the desired noise reduction. The maximum rotational speed threshold of the motorised handpiece shown in FIG. 5a for acceptable noise and heat generation is presently approximately 40,000-50,000 min.sup.-1.
As a result of the two drive shafts 109, 110 coupled together via the mechanical driver system 111, there is increased wear to the two drive shafts 109, 110 in the region of the driver system 111 over time. Furthermore, increased vibration occurs during operation of the motorised handpiece 101 owing to the relatively low overall rigidity of the shaft arrangement produced by the use of the two separate drive shafts 109, 110. Vibrations of this type can result in the so-called white finger syndrome in the user. In this case, blood is forced away from the finger tips of the user who is holding the motorised handpiece 101 with his finger tips in the region of the motorised handpiece part 113, for example, thus causing the finger tips to become white.
FIGS. 5b shows a further known motorised handpiece, which is marketed by the Applicants, for example, under the name "SF motor spindle type 4010". The motorised handpiece 101 shown in FIG. 5a comprises an integrally formed housing 112, in which a motor, for example a three-phase synchronous motor or a collector-free d.c. motor, is again arranged with a short-circuit ring 102, a stator winding 103 and a rotor magnet 104. As in FIG. 5a, the rotor magnet 104 is also fitted on a drive shaft 106 in the motorised handpiece 101 according to FIG. 5b. This drive shaft 106 is constructed as a hollow shaft and at its tool end has a conical internal shape, which, as in FIG. 5a, matches the conical external shape of the sleeve-shaped, slotted clamping jaw 105. This clamping jaw 105 is again part of a tool clamping system, which is arranged inside the hollow shaft 106. To this end, the clamping jaw 105 is integrally constructed with or coupled to a further drive shaft 110, the drive shaft 110 comprising an external thread 120 at one end, which engages in an internal thread of the hollow shaft 106. When the motor is inoperative, the drive shaft 110 with the clamping jaw 105 can be actuated by a rotary knob 121 arranged on the rear part of the motorised handpiece 101, i.e. can be screwed into or out of the hollow shaft 106 in the longitudinal direction. As a result of the conical external shape of the clamping jaw 105, which is designed to match the conical internal shape of the hollow shaft 106, the clamping jaw 105 is compressed as the clamping jaw 105 is screwed with the drive shaft 110 into the hollow shaft 106, so that a tool 108, which is located in the clamping jaw 105 and of which only the tool shaft is indicated in FIG. 5b, is held in a force-locking manner by the clamping jaw 105. Accordingly, when the clamping jaw 105 is screwed out of the hollow shaft 106, the tool 108 is released again from the clamping jaw 105. The motorised handpiece 101 shown in FIG. 5b is suitable, for example, for motor rotational speeds in the region of 60,000 min.sup.-1.
The motorised handpiece 101 shown in FIG. 5b has an integral construction and therefore has the advantage that it is only necessary to mount the hollow shaft 106 with the aid of two ball bearings 114, 115. Although the drive shaft 106 is mechanically coupled to the other drive shaft 110 as in FIG. 5a as a result of the screw connection between the internal thread 119 and the external thread 120, no driver system 111 of the type shown in FIG. 5a is required in the motorised handpiece 101 shown in FIG. 5b. Consequently, it is possible to make full use of the clearance provided by the bearings 114, 115 and the motor 102-104 with regard to the rotational speed which can be attained. However, a three-phase synchronous motor is conventionally used for the motorised handpiece shown in FIG. 5b, which requires a cooling fan for efficiency reasons and also in view of the rotational speeds which can be attained. The cooling fan generates a relatively high level of noise, in particular in high rotational speed ranges. In addition, the tool clamping system of the motorised handpiece 101 shown in FIG. 5b is awkward from an ergonomic point of view, since an additional rotary knob 121, which has to be manually actuated, is required in order to clamp the tool 108.